Pure Glue Research Articles

Fourier transform infrared spectroscopic study of rabbit glue/inorganic pigments mixtures in fresh and aged reference paint reconstructions

We studied the interactions of rabbit glue, a collagen-based proteinaceous binder, with azurite (Cu3(CO3)2(OH)2), calcium carbonate (CaCO3), hematite (Fe2O3·nH2O), red lead (Pb3O4) and cinnabar (HgS) by Fourier transform infrared spectroscopy (FT-IR). The research was carried out on a set of paint reconstructions, which were analysed before and after artificial light ageing. A deconvolution of the amide I FT-IR absorption peak was performed with a written-in-house LabVIEW program to study the secondary structure of the glue.The changes in the glue conformation highlighted that all the inorganic pigments interact with the proteinaceous binder. The conformational changes were correlated with a loss of stability of the collagen structure, especially after ageing, likely due to the interlayer coordination of metals salts and oxide with protein functional groups. These results were correlated with the lower thermal stability of the glue/pigment mixtures with respect to the pure glue, evidenced by thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses performed in a previous step of this work.

Hadron Spectroscopy with CLAS and CLAS12

The CLAS detector completed a highly successful data-taking lifetime in 2012. The mass range accessible with the CEBAF 6 GeV electron beam and the large solid angle of the detector made it the premier facility for studying baryon resonances. The analysis of a great number of final states with differing polarization states is underway and will lead to a greater understanding of the existing nucleon resonances. In the meantime, preparation for an upgraded detector, CLAS12, is progressing. With commissioning due to start in 2016 with a 11 GeV electron beam CLAS12 will kinematically favour the study of mesons. In particular, it will look to resolve outstanding questions as to the make-up of mesonic states in terms of hybrid states with gluonic constituents; states of pure glue; or tetraquark/molecular configurations.

Two-loop perturbative corrections to the thermal effective potential in gluodynamics

The thermodynamics of pure glue theories can be described in terms of an effective action for the Polyakov loop. This effective action is of the Landau-Ginzburg type and its variables are the angles parametrizing the loop. In this paper we compute perturbative corrections to this action. Remarkably, two-loop corrections turn out to be proportional to the one-loop action, independent of the eigenvalues of the loop. By a straightforward generalization of the 't Hooft coupling this surprisingly simple result holds for any of the classical and exceptional groups.

LargeNcdeconfinement transition in the presence of a magnetic field

We investigate the effect of a homogeneous magnetic field on the thermal deconfinement transition of QCD in the large ${N}_{c}$ limit. First we discuss how the critical temperature decreases due to the inclusion of ${N}_{f}\ensuremath{\ll}{N}_{c}$ flavors of massless quarks in comparison to the pure glue case. Then we study the equivalent correction in the presence of an external Abelian magnetic field. To leading order in ${N}_{f}/{N}_{c}$, the deconfinement critical temperature decreases with the magnetic field if the flavor contribution to the pressure behaves paramagnetically, with a sufficiently large magnetization as to overcome any possible magnetic effects in the string tension. Finally, we discuss the effects from a finite quark mass and its competition with magnetic effects.

Roberge-Weiss transition and ’t Hooft loops

Roberge and Weiss showed that for $SU(N)$ gauge theories, phase transitions occur in the presence of an imaginary quark chemical potential. We show that at asymptotically high temperature, where the phase transition is of first order, that even with dynamical quarks 't Hooft loops of arbitrary $Z(N)$ charge are well defined at the phase boundary. To leading order in weak coupling, the 't Hooft loop satisfies Casimir scaling in the pure glue theory, but not with quarks. Because the chemical potential is imaginary, typically the interaction measure is negative on one side of the phase transition. Using a matrix model to model the deconfining phase transition, we compute the phase diagram for heavy quarks, in the plane of temperature and imaginary chemical potential. In general we find intersecting lines of first order transitions. Using a modified Polyakov loop which is Roberge-Weiss symmetric, we suggest that the interface tension is related to the 't Hooft loop only at high temperature, where the imaginary part of this Polyakov loop, and not the real part, is discontinuous across the phase boundary.

Chiral polarization scale of QCD vacuum and spontaneous chiral symmetry breaking

It has recently been found that dynamics of pure glue QCD supports the low energy band of Dirac modes with local chiral properties qualitatively different from that of a bulk: while bulk modes suppress chirality relative to statistical independence between left and right, the band modes enhance it. The width of such chirally polarized zone – chiral polarization scale ∧ch – has been shown to be finite in the continuum limit at fixed physical volume. Here we present evidence that ∧ch remains non-zero also in the infinite volume, and is therefore a dynamical scale in the theory. Our experiments in Nf = 2+1 QCD support the proposition that the same holds in the massless limit, connecting ∧ch to spontaneous chiral symmetry breaking. In addition, our results suggest that thermal agitation in quenched QCD destroys both chiral polarization and condensation of Dirac modes at the same temperature Tch > Tc.

Neonatal Dural Arteriovenous Fistula at the Confluence Presenting with Paralysis of the Orbicularis Oris Muscle

A male neonate presented a dural arteriovenous fistula (DAVF) at the confluence with paralysis of the orbicularis oris muscle. The interesting features in our case were the clinical symptoms (orbicularis oris muscle paralysis at birth), angioarchitecture (high-flow arteriovenous shunts at the confluence) and the size and hemodynamic flow (mid-sized venous pouch) of the fistula. Additionally, the embolization technique (i.e., occipital artery approach, closing shunts with pure glue) automatically resulted in the immediate and complete closure of accessory feeders without any additional treatment, and the midterm clinical outcome was good. We succeeded improving the symptoms of a neonate with a congenital high-flow DAVF by closing a fistula using a small amount of glue.

Critical endpoint for deconfinement in matrix and other effective models

We consider the position of the deconfining critical endpoint, where the first order transition for deconfinement is washed out by the presence of massive, dynamical quarks. We use an effective matrix model, employed previously to analyze the transition in the pure glue theory. If the param- eters of the pure glue theory are unaffected by the presence of dynamical quarks, and if the quarks only contribute perturbatively, then for three colors and three degenerate quark flavors this quark mass is very heavy, m_de \sim 2.5 GeV, while the critical temperature, T_de, barely changes, \sim 1% below that in the pure glue theory. The location of the deconfining critical endpoint is a sensitive test to differentiate between effective models. For example, models with a logarithmic potential for the Polyakov loop give much smaller values of the quark mass, m_de \sim 1 GeV, and a large shift in T_de \sim 10% lower than that in the pure glue theory.

Comments on a Minimal Quasiparticle Approach for the QGP and Its Large-N c Limits

A minimal quasiparticle approach for describing QGP at temperatures much higher than the critical one is discussed. It involves an ideal-gas framework in which quark and gluon masses depend on temperature. This model is able to reproduce the recent equations of state computed in lattice QCD for temperatures typically higher than 2 Tc, in a range in which it is reasonable to neglect interactions between quasiparticles. In addition, the equations of state for a generic gauge theory with gauge groups SU(Nc) and quarks in an arbitrary representation are studied. The gauge independence in the pure glue sector and the large-Nc equivalence between the gauge groups SU(Nc) and SO(2Nc) in a full plasma is finally shown for normalized thermodynamic quantities.

Bulk viscosity of anisotropically expanding hot QCD plasma

The bulk viscosity, $\ensuremath{\zeta}$ and its ratio with the shear viscosity, $\ensuremath{\zeta}/\ensuremath{\eta}$ have been studied in an anisotropically expanding pure glue plasma in the presence of turbulent color fields. It has been shown that the anisotropy in the momentum distribution function of gluons, which has been determined from a linearized transport equation eventually leads to the bulk viscosity. For the isotropic (equilibrium) state, a recently proposed quasiparticle model of pure $SU(3)$ lattice QCD equation of state has been employed where the interactions are encoded in the effective fugacity. It has been argued that the interactions present in the equation of state, significantly contribute to the bulk viscosity. Its ratio with the shear viscosity is significant even at $1.5{T}_{c}$. Thus, one needs to take in account the effects of the bulk viscosity while studying the hydrodynamic expansion of quark-gluon plasma in the Relativistic Heavy Ion Collider and the Large Hadron Collider.

High-flow Neonatal Macrocerebral Arteriovenous Fistulas in Hereditary Hemorrhagic Telangiectasia

Although some cases of vein of Galen aneurysmal malformation (VGAM) present initial clinical symptoms such as cardiopulmonary disturbance in the neonatal period, pial arteriovenous fistula is very seldom present as a clinical symptom immediately after birth. A neonatal patient, the first-born to his family, presented with tachypnea postpartum. This baby had a family history of hereditary hemorrhagic telangiectasia. A cerebral MR image revealed multiple macrocerebral arteriovenous fistulas (MCAVFs), resulting in a large partially thrombosed venous pouch within the cerebral cortex. Trans-arterial embolizations of the main two fistulas were performed using N-butyl cyanoacrylate (NBCA) with tantalum powder six months after birth. Post-embolization angiography confirmed the obliteration of the fistulas and magnetic resonance imaging (MRI) revealed thrombosis and reduction in size of the venous component. His tachypnea disappeared completely. There were no neurological complications due to the treatment. The prognosis of multiple MCAVFs mainly depends on the presence of medullar signs and symptoms and a delay before treatment. Pure glue endovascular intervention, as used in our case, is considered to be the first therapeutic choice to decrease the risk of neurological consequences.

Shear and bulk viscosities for pure glue matter

Shear $\eta$ and bulk $\zeta$ viscosities are calculated in a quasiparticle model within a relaxation time approximation for pure gluon matter. Below $T_c$ the confined sector is described within a quasiparticle glueball model. Particular attention is paid to behavior of the shear and bulk viscosities near $T_c$. The constructed equation of state reproduces the first-order phase transition for the glue matter. It is shown that with this equation of state it is possible to describe the temperature dependence of the shear viscosity to entropy ratio $\eta/s$ and the bulk viscosity to entropy ratio $\zeta/s$ in reasonable agreement with available lattice data but absolute values of the $\zeta/s$ ratio underestimate the upper limits of this ratio in the lattice measurements typically by an order of magnitude.

Heavy quark free energy in QCD and in gauge theories with gravity duals

We show that the Polyakov loop approaches its asymptotic value at high temperatures {\it from below} in any strongly-coupled gauge theory at large $N_c$ with a dual supergravity description. In these theories the Polyakov loop can be used to define a quantity that behaves as a free energy of a heavy quark in the medium. This should be compared to the recent lattice results in pure glue SU(3) theory at high temperatures where the Polyakov loop approaches its non-interacting limit {\it from above}. We show that the "heavy quark free energy" obtained from the renormalized loop computed on the lattice does not behave as a true thermodynamic free energy. We conjecture that this should always be the case in asymptotically free gauge theories.

Glueballs, gluon condensate, and pure glue QCD below T c

A quasiparticle description of pure glue QCD thermodynamics at T<T_c is proposed and compared to recent lattice data. Given that a gas of glueballs with constant mass cannot quantitatively reproduce the early stages of the deconfinement phase transition, the problem is to identify a relevant mechanism leading to the observed sudden increase of the pressure, trace anomaly, etc. It is shown that the strong decrease of the gluon condensate near T_c combined with the increasing thermal width of the lightest glueballs might be the trigger of the phase transition.

A study of the interaction between rabbit glue binder and blue copper pigment under UV radiation: A spectroscopic and PCA approach

The effects of a UV-accelerated ageing test on model samples of azurite glue tempera, pure azurite and pure rabbit glue, all elaborated according to medieval recipes, were studied. The color changes and modifications in composition and texture for both pure and mixed samples are shown and discussed. Special attention is given to the physico-chemical interactions occurring when azurite and glue are combined. Ageing effects on the model samples after up to 3000 h of UV irradiation were periodically analyzed by scanning electron microscopy (SEM) with X-ray energy dispersive spectrometer (EDS) microanalysis, X-ray diffraction (XRD), reflectance spectrophotometry and Fourier-transform infrared spectroscopy (FT-IR). Once the ageing process ended, a chemometric study using principal component analysis (PCA) of the FT-IR data was carried out independently for every model sample and for all the azurite-laden samples. Loadings from the significant principal components were analyzed to identify the FT-IR frequency (cm −1) involved in the degradation process. PCA proved capable of identifying significant changes in pure glue samples. Also this work showed the lack of photochemical effects of UV irradiation on both pure azurite samples and those mixed with glue, in agreement with the SEM-EDS, XRD and colorimetrics results. Nevertheless PCA revealed that the azurite FT-IR spectral variability decreased in the presence of glue, being more affected by exposure to the IR region between 2100 cm −1 and 3600 cm −1, where the azurite band is located. In addition, PCA managed to separate the azurite/glue mixture samples from pure azurite samples.

QCD tests with an infrared finite gluon propagator and coupling constant

Recent progress in the solution of Schwinger-Dyson equations, as well as lattice simulation of pure glue QCD, indicate that the gluon propagator and coupling constant are infrared finite. Such non-perturbative information can be introduced in the QCD perturbative expansion in the scheme named Dynamical Perturbation Theory. We exemplify this procedure with the calculation of some two-body non-leptonic annihilation B meson decays, which show agreement with the experimental data in the case of a gluon propagator characterized by a dynamical gluon mass of 500MeV, compatible with the value found in several processes computed with this method. We give a preliminary account of the application of this procedure at the loop level in the case of the Bjorken sum rule.

Gluon structure function of a color dipole in the light-cone limit of lattice QCD

We calculate the gluon structure function of a color dipole in near-light-cone $SU(2)$ lattice QCD as a function of ${x}_{B}$. The quark and antiquark are external nondynamical degrees of freedom which act as sources of the gluon string configuration defining the dipole. We compute the color dipole matrix element of transversal chromo-electric and chromo-magnetic field operators separated along a direction close to the light cone, the Fourier transform of which is the gluon structure function. As vacuum state in the pure glue sector, we use a variational ground state of the near-light-cone Hamiltonian. We derive a recursion relation for the gluon structure function on the lattice similar to the perturbative Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equation. It depends on the number of transversal links assembling the Schwinger string of the dipole. Fixing the mean momentum fraction of the gluons to the ``experimental value'' in a proton, we compare our gluon structure function for a dipole state with four links with the next-to-leading-order MRST 2002 and the CTEQ AB-0 parametrizations at ${Q}^{2}=1.5\text{ }\text{ }{\mathrm{GeV}}^{2}$. Within the systematic uncertainty we find rather good agreement. We also discuss the low ${x}_{B}$ behavior of the gluon structure function in our model calculation.

Improved holographic Yang–Mills at finite temperature: Comparison with data

The semi-phenomenological improved holographic model for QCD is confronted with data of the pure glue, large- N c gauge theory. After fitting two phenomenological parameters in the potential, the model can reproduce in detail all thermodynamic functions at finite temperature. It also reproduces in detail all known spin-0 and spin-2 glueball observables at zero temperature and predicts the rest of the 0 + + and 2 + + towers. A similar two parameter fit in the CP-odd sector postdicts the correct second 0 + − glueball mass, and predicts the rest of the 0 + − tower.

Reparametrization invariant collinear operators

In constructing collinear operators, which describe the production of energetic jets or energetic hadrons, important constraints are provided by reparametrization invariance (RPI). RPI encodes Lorentz invariance in a power expansion about a collinear direction, and connects the Wilson coefficients of operators at different orders in this expansion to all orders in ${\ensuremath{\alpha}}_{s}$. We construct reparametrization invariant collinear objects. The expansion of operators built from these objects provides an efficient way of deriving RPI relations and finding a minimal basis of operators, particularly when one has an observable with multiple collinear directions and/or soft particles. Complete basis of operators is constructed for pure glue currents at twist-4, and for operators with multiple collinear directions, including those appearing in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}3$ jets, and for $pp\ensuremath{\rightarrow}2$ jets initiated via gluon fusion.

Cosmology of bifundamental fields

If a field theory contains gauged, non-Abelian, bifundamental fields, i.e. fields that are charged under two separate non-Abelian gauge groups, the transition from a deconfined phase to a hadronic phase may be frustrated. Similar frustration may occur in non-Abelian gauge models containing matter only in higher dimensional representations, e.g. models with pure glue, or if ordinary quarks are confined by two flux tubes, as implied in the triangular configuration of baryons within QCD. In a cosmological setting, such models can lead to the formation of a web of confining electric flux tubes that can potentially have observational signatures.